Rheology modifiers are often used in formulations, such as detergents, paints and cosmetic products, e.g., hair and skin care products. Depending on the application, different types of rheology modifiers can be added to these formulations to tailor the theological properties of the product to obtain the desired flow characteristics (viscoelasticity) and sensorial effects.
Some classes of rheological modifiers include electrolytes and associative polymers. Electrolytes can be added to formulations, such as personal care formulations, which tend to be based on concentrated surfactant systems consisting of a mixture of anionics such as alkyl sulfates, amphoterics and other ingredients. Addition of electrolytes (typically NaCl) can cause a change in the micellar structure of the surfactant molecules, e.g., from spherical to rod-shaped units, which subsequently grow and form a “gel” network, thereby increasing the viscosity of the formulation. However, the addition of salt does not always give rise to optimum rheological characteristics and can result in formulations that are stringy and rubbery in appearance.
Associative polymers are water soluble polymers containing hydrophobic moieties (e.g., hydrocarbon groups). In surfactant systems, associative polymers can form network-like supramolecular structures at relatively lower polymer concentration due to non-covalent bonding interactions between hydrophobic moieties. Apart from the hydrophobic binding interactions, associative polymers can also be modified to include other forms of interactions with surfactant micelles, such as ion-dipole and/or ion-ion attractions, that can lead to the formation of a network-like supramolecular structure comprising, e.g., associative polymers, solvent, salts, and surfactants, resulting in an increase in the viscosity of the formulation.
Apart from the chemical composition of the rheology modifier, other factors can affect the viscosity of the rheology modifier/surfactant system, such as pH, the concentration of the surfactant, and the concentration of the rheology modifier.
One limitation of conventional rheology modifier/surfactant systems is that at high concentrations of the surfactant, the network-like structure between the surfactant and rheology modifier is disrupted, which can decrease the mixture's viscosity. Furthermore, conventional rheology modifier/surfactant systems can require high concentrations of the rheology modifier to achieve a desirable viscosity while maintaining acceptable sensorial characteristics.
Accordingly, there exists a need to provide an effective rheology modifier capable of increasing the viscosity of a surfactant system at low concentrations of surfactant and rheology modifier, enhancing the rheological stability of the formulation, and which provides desirable sensorial effects in various applications.